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Chapter 9: Masks and Extractions
Selecting Using Masks
Most Photoshop users don't use masks. If my personal experience is any indication, it's not only because masks seem complicated but also because they strike most folks as being more trouble than they're worth. Like nearly everyone, when I first started using Photoshop, I couldn't even imagine a possible application for a mask. I have my lasso tool and my magic wand. If I'm really in a rut, I can pull out my pen tool. What more could I possibly want?Quite a bit, as it turns out. Every one of the tools I just mentioned is only moderately suited to the task of selecting images. The lasso tools let you create free-form selections, but none of the tools — not even the magnetic lasso — can account for differences in focus levels. The magic wand selects areas of color, but it usually leaves important colors behind, and the edges of its selection outlines often appear ragged and ugly. The pen tool is extremely precise, but it results in mechanical outlines that may appear incongruous with the natural imagery they contain.Masks offer all the benefits of the other tools. With masks, you can create free-form selections, select areas of color, and generate amazingly precise selections. Masks also address all the deficiencies associated with the selection tools. They can account for different levels of focus, they give you absolute control over the look of the edges, and they create selections every bit as natural as the image itself.
In fact, a mask is the image itself. Masks use pixels to select pixels. Masks are your way to make Photoshop see what you see using the data inherent in the photograph. Masks enable you to devote every one of Photoshop's powerful capabilities to the task of creating a selection outline. Masks are, without a doubt, the most accurate selection mechanism available in Photoshop.If you're not entirely clear about what I mean by the term mask, I'll tell you: A mask is a selection outline expressed as a grayscale image.
Selected areas appear white.
Deselected areas appear black.
Partially selected parts of the image appear gray. Feathered edges are also expressed in shades of gray, from light gray near the selected area to dark gray near the deselected area.
Figure 9-1 shows a selection outline and its equivalent mask. The top example shows an elliptical selection outline that I feathered by choosing Select Feather. Below this example is the same selection expressed as a mask. The selected area is white and is said to be unmasked; the deselected area is black, or masked. Note that although you can't see the feathering effect in the selection outline — marching ants can't accurately express softened edges — in the equivalent mask it's completely visible.
Figure 9-1: A feathered selection outline (top) and its equivalent mask (bottom).
When you look at the mask at the bottom of Color Plate 9-1.) Areas covered with the rubylith are masked (deselected); areas that appear normal — without any red tint — are unmasked (selected). When you return to the standard marching ants mode, any changes you make to your image affect only the unmasked areas.
Figure 9-2: Here is the mask from Figure 9-1, shown as it appears when viewed along with the image.
Now that you know roughly what masks are (the definition becomes progressively clearer throughout this chapter), the question remains, what good are they? Because a mask is essentially an independent grayscale image, you can edit the mask using paint and edit tools, filters, color-correction options, and almost every other Photoshop function. You can even use the selection tools, as discussed in the previous chapter. With all these features at your disposal, you can't help but create a more accurate selection outline in a shorter amount of time.
